In audio amplifiers, the bandwidth limitations introduced by compensation are still far beyond the audio frequency range, and the slew rate limitations can be configured such that full amplitude 20 kHz signal can be reproduced without the signal encountering slew rate distortion, which is not even necessary for reproducing actual audio material.
42.
The slew rate depends both on the gradient coil ( it takes more time to ramp up or down a large coil than a small coil ) and on the performance of the gradient amplifier ( it takes a lot of voltage to overcome the inductance of the coil ) and has significant influence on image quality.
43.
Slewing is usually caused by the input stage saturating; the result is a constant current driving a capacitance in the amplifier ( especially those capacitances used to implement its frequency compensation ); the slew rate is limited by " i " / " C " } } . Slewing is associated with the " large-signal " performance of an op-amp.
44.
This was done in order to reduce the quantization error, and is accomplished in part by changing the effective " step size " of the encoder based on previously recorded information . ( Thereby increasing or decreasing the slew rate . ) The system also has two analog pre-processing steps which compress the input signal in both the amplitude and frequency domain, in order to more closely match the abilities of the encoder.
45.
Thus, if one were to measure the output, it would be a 5 V, 100 kHz sawtooth, rather than a 10 V, 100 kHz sawtooth . Next consider the same amplifier and 100 kHz sawtooth, but now the input amplitude is 100 mV rather than 1 V . After 10x amplification the output is a 1 V, 100 kHz sawtooth with a corresponding slew rate of 0.1 V per microsecond.
46.
The slew rate limitation of the operational amplifier used to create the absolute value ( especially at low input signal levels ) tends to make the second method the poorest at high frequencies, while the FET method can work close to VHF . Specialist techniques are required to produce sufficiently accurate integrated circuits for complex analog calculations, and very often meters equipped with such circuits offer true RMS conversion as an optional extra with a significant price increase.
